The typical drain in the bottom of a swimming pool is a flushmounted grate, with relatively small rectangular or circular openings in the grate. The grate covers a circular drain opening, which extends through the floor of the swimming pool and is attached to a drain pipe (typically of 2" to 4" in diameter). The drain pipe is connected with the recirculating pump of the pool, which removes water through the drain of the pool, to supply that water through a filtration system and, ultimately, back to return lines for the pool. A relatively large volume of water is moved through the drain while the pump is operating. The grate placed in the opening of the drain is designed to prevent leaves and other debris from passing through the main drain, since such leaves can clog the leaf catching basket, which usually is placed between the intake of the pump and the drain.
In addition, conventional swimming pool drains can produce a whirlpool vortex as a result of the suction of water passing outwardly through the drain pipe at the bottom of the drain pot or drain housing. It is possible for such a vortex to have sufficient force that the hair or other body portions of a swimmer, can be sucked downwardly by the vortex and be trapped by the suction of the drain. This is a significant safety problem with the past designs of some swimming pool drain systems.
Swimming pool drains, which have been used in the past, also are not adjustable to regulate the size of the openings in the cover or to regulate the amount of water flow which may take place through the drain. Once such drains are in place, they remain fixed. The size of the openings and the water flow rate are determined in advance of the construction of the pool into which the drain is placed.
A drain designed to facilitate the flow of water through the drain cover and into a drain pot is disclosed in three patents to Sisk U.S. Pat. Nos. 2,695,073; 2,695,678; and 2,777,532. The drain pot disclosed in these patents is constructed with a support rim around it for holding the drain cover. The support rim has a number of arcuate slots in it to facilitate the flow of water through the slots down the sides of the drain. The cover then fits over the large drain opening, and is in the form of a generally standard slotted grate. There is no provision in any of the Sisk patents for adjusting the size of the slots or the size of the opening between the cover and the lip of the drain pot.
The patent to Clapp No. U.S. Pat. No. 149,373 discloses a drain cover or grating which is similar in constructional aspects to the ones disclosed in the Sisk patents. The drain system of Clapp, however, has a cover which is concave in shape, and protrudes above the surface of the area surrounding the drain pot.
The patent to Lunden U.S. Pat. No. 4,492,491 is directed to a drain or roof outlet for rainwater. The cover of the outlet or drain of Lunden fits in the center of the drain; so that the water flow enters into the drain around the edges of the cover between the edges and the edge of the drain pot. The cover itself, however, is made of screen material; so that water also can flow through the cover, as well as around the edges of the cover.
It is desirable to provide an anti-vortex drain, particularly suited for a flush-mounted swimming pool drain, which is of simple construction and easy to install.